onsemi BUD42DT4

Overview

BUD42DT4 from onsemi is a high-speed, high-gain bipolar NPN transistor with integrated antisaturation network and transient voltage suppression capability, rated for 650 V_CEO, 4 A continuous collector current, and 25 W power dissipation in DPAK (Case 369C) surface-mount package - designed for light ballast and inductive switching applications requiring fast turn-off and robust safe operating area.

For engineers reviewing the BUD42DT4 datasheet, pinout, applications, or equivalent options, this page delivers verified electrical specs, thermal behavior, switching timing under clamped inductive loads, built-in freewheeling diode characteristics, and real-world selection guidance for high-voltage switching circuits.

Technical Context

The BUD42DT4 integrates an internal freewheeling diode between emitter and collector, enabling self-protected inductive load commutation without external diodes. Its antisaturation network ensures low dynamic saturation voltage during switching transitions while maintaining flat DC current gain across operating conditions.

It operates with tight parameter spreads enabled by "6 Sigma" manufacturing, supports clamped inductive switching up to 300 V with controlled storage time (t_si ≤ 4 µs at h_FE = 5), and features ESD protection rated at 3B per HBM - all within a thermally optimized DPAK package with R_JC = 5.0 °C/W.

Key Specifications

Pinout & Package

DPAK (Case 369C) surface-mount package with 4-terminal configuration: exposed collector tab (pins 2 and 4) provides low-inductance, high-current path and thermal interface; pin 1 is base, pin 3 is emitter.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN switching transistor applications.

Compared with MJE13003G and BU508AF, the BUD42DT4 uniquely combines integrated freewheeling diode, antisaturation logic, and DPAK thermal performance - making it the only option among the three qualified for compact, high-reliability electronic ballast designs requiring <7 µs turn-off and <1.0 V saturation.

Availability

BUD42DT4 is available at Aetrix Electronics and suitable for compact fluorescent lamp ballasts, LED driver primary switches, inductive relay drivers, and AC motor speed control modules requiring stable component supply, long-lifecycle support, and Pb-free compliance.

Supply support for BUD42DT4 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensor, and connectivity solutions for automotive, industrial, and consumer markets.

The BUD42DT4 belongs to onsemi's high-voltage bipolar transistor product line, engineered specifically for lighting control and inductive switching applications demanding high V_CEO, fast switching, and integrated protection features.

FAQ

What is the maximum clamped inductive voltage the BUD42DT4 can safely handle?

The BUD42DT4 is validated for clamped inductive switching up to 300 V with reverse-biased base (V_BE(off) = −1.5 V to −5 V), as defined in its Reverse Bias Safe Operating Area (RBSOA) curve. Its V_CEO(sus) rating of 350 Vdc applies under resistive-load test conditions with L = 25 mH. Exceeding 300 V in clamped inductive operation risks second breakdown unless external clamping is added.

Does the BUD42DT4 require an external freewheeling diode in lamp ballast circuits?

No - the BUD42DT4 includes a built-in freewheeling diode between emitter and collector (VEC = 0.9–1.5 V at 1.0 A), eliminating the need for an external diode in standard CFL and LED driver topologies. This integration reduces bill-of-materials count, PCB area, and potential failure points associated with discrete diode placement and solder joint reliability.

How does the antisaturation network in the BUD42DT4 improve switching performance?

The antisaturation network in the BUD42DT4 actively limits base-collector forward bias during turn-on, reducing stored charge and cutting storage time (t_si) to ≤4 µs at h_FE = 5. This results in faster turn-off (t_off = 4.6–6.55 µs), lower dynamic saturation voltage (V_CE(dsat) = 0.35 V at 1 A after 3 s), and reduced switching losses compared to standard NPN transistors without such networks.

What is the thermal resistance from junction to case (R_JC) for the BUD42DT4, and how should it be used in heatsink design?

The BUD42DT4 has a maximum R_JC of 5.0 °C/W, measured from junction to the exposed collector tab (pins 2 and 4). In heatsink design, this value must be combined with heatsink-to-ambient resistance (R_HA) and interface thermal resistance (R_INT) to calculate total thermal resistance. For example, at 20 W dissipation and T_J(max) = 150°C, a heatsink with R_HA ≤ 4.0 °C/W is required when using a typical thermal pad (R_INT ≈ 0.5 °C/W).

Is the BUD42DT4 pin-compatible with other DPAK-packaged transistors like the MJD122 or MJD127?

No - the BUD42DT4 uses a 4-pin DPAK (Case 369C) with dual collector terminals (pins 2 and 4), whereas MJD122/MJD127 use standard 3-pin DPAK (Case 369) with single collector. Pin 1 (base), pin 2 (collector), and pin 3 (emitter) assignments differ, and the BUD42DT4's pin 4 is not present on those parts. PCB layout and footprint must be redesigned to accommodate the 4-terminal configuration and exposed collector tab routing.